The present invention relates to an impact detecting circuit that detects an impact on the basis of an output signal of an impact sensor, an impact detecting apparatus including the impact sensor and the impact detecting circuit, and a recording and reproducing apparatus including the impact detecting apparatus.
A 2.5-inch or smaller HDD (Hard Disk Drive) apparatus included in a portable apparatus, such as a notebook personal computer (so-called notebook PC) or the like, includes an impact sensor and an impact detecting circuit. The impact sensor and the impact detecting circuit are provided to prevent the destruction of recorded information, for example, when a head unit in a recording mode moves on impact to an area where information is already recorded and performs a recording operation at that position.
The HDD apparatus is a kind of recording and reproducing apparatus for recording information on a disk-shaped recording medium and reproducing the recorded information from the recording medium. The HDD apparatus uses a hard disk as the recording medium. An outline of a configuration of the HDD apparatus will be described with reference to FIG. 3.
In FIG. 3, a head unit for recording information and reproducing the recorded information on a disk is disposed within an enclosure 1. The head unit is formed by a recording head (for example, an inductive head) and a reproducing head (for example, a magnetoresistive head). The head unit is supported by a head arm 4, so as to be movable in a direction of a radius of the disk. A signal to be recorded on the disk or a signal read from the disk is transferred between the head unit and a signal processing IC (recording/reproducing IC) 3 included within the enclosure 1.
With the HDD apparatus thus formed, an impact sensor is conventionally mounted on a main board external to the enclosure 1. The main board is mounted with an impact detecting circuit (IC) for processing a signal from the impact sensor and outputting a detection signal when detecting an impact of a predetermined value or higher and other circuits.
However, when the impact sensor is mounted on the main board external to the enclosure 1, as described above, the board somewhat absorbs the force of an impact because the board is generally flexible. Therefore, it is not possible to detect the impact accurately. In addition, while a part around the head unit is to be protected from an impact, the impact sensor is mounted at a position distant from the head unit. From such a viewpoint, it is desirable to dispose the impact sensor within the enclosure 1.
Also, there has recently been a trend toward smaller HDD apparatus, for example, 1.8-inch and 1-inch HDD apparatuses. When the HDD apparatus thus becomes smaller, the main board attached to the enclosure 1 naturally becomes smaller too, thus reducing the space (both area and height) for disposing the impact sensor. Also from this viewpoint, it is necessary to dispose the impact sensor within the enclosure 1.
On the other hand, it may be said to be desirable to dispose the impact detecting circuit at a position adjacent to the impact sensor. This is because a signal generated on impact from the impact sensor is very weak, and noise tends to be superimposed on a long transmission line between the impact sensor and the impact detecting circuit, so that erroneous operation due to the noise needs to be prevented.
However, since the signal processing IC (recording/reproducing IC) 3 is included within the enclosure 1, as described above, the enclosure 1 actually has no space for disposing the impact detecting circuit (IC). Accordingly, integration of the recording/reproducing IC and the impact detecting IC into a single chip is conceivable. In the following, a circuit configuration of an impact detecting circuit according to a conventional example will be described.
FIG. 4 is a circuit diagram showing an example of a circuit configuration of an impact detecting circuit according to a conventional example. An impact sensor 111 in FIG. 4 outputs a first-order differential current in proportion to impact strength. The first-order differential current is subjected to first-order integration by an integrating circuit 115 formed by an operational amplifier 112, a capacitor 113, and a resistance 114 and converted into a voltage with a flat frequency characteristic.
Then, an LPF (Low Pass Filter) 116 cuts off a high-frequency component unnecessary for impact detection, and then the result is amplified by an amplifier 117. A HPF (High Pass Filter) 118 having a sufficiently low cutoff frequency eliminates a DC offset component, and then the result is supplied to a comparator 119 as a non-inverting (+) input of the comparator 119. The comparator 119 uses a threshold level Vth as an inverting (xe2x88x92) input of the comparator 119. An impact detection level is set by adjusting the threshold level Vth.
In this case, for example, supposing that an impact of 1 G and 1 kHz is applied, the impact sensor 111 outputs a current of a magnitude of 1 nA, and the integrating circuit 115 outputs a voltage of a magnitude of 1 mV.
When the thus formed impact detecting circuit is used as it is to be integrated into a single chip with the recording/reproducing IC as described above, the following problem occurs. When a recording driver included in the recording/reproducing IC operates, an input offset voltage Voff occurs at the operational amplifier 112, as shown in the equivalent circuit of FIG. 5. The impact sensor 111 is a capacitance in terms of the equivalent circuit. Hence, the input offset voltage Voff is inputted to the integrating circuit 115 as a current differentiated by the capacitance of the impact sensor 111.
An experiment by the present inventor shows that the current reaches 100 nA or greater. As a result, letting Ch be a capacitance value of the capacitor 113 and Rh be a resistance value of the resistance 114, a large voltage waveform with a time constant Ch*Rh is generated at an output terminal of the integrating circuit 115, as shown in the waveform diagram of FIG. 6. Thus, an erroneous detection occurs each time the recording driver is operated in the recording mode.
The above problem can be solved if the input offset voltage Voff itself is eliminated. However, the input offset voltage Voff is caused by noise within the recording/reproducing IC resulting from the operation of the recording driver. It is therefore difficult to reduce the input offset voltage Voff to 0 mV. There will be a trend in the future for the input offset voltage Voff to be increased with an increase in the speed of the recording driver. The input offset voltage Voff thus presents a problem in integrating the impact detecting circuit into a single chip with the recording/reproducing IC.
The present invention has been made in view of the above problem, and it is accordingly an object of the present invention to provide an impact detecting circuit, an impact detecting apparatus, and a recording and reproducing apparatus including the same that can eliminate erroneous detection resulting from the input offset voltage Voff of the integrating circuit and perform impact detection more reliably when the impact detecting circuit is integrated into a single chip with the recording/reproducing IC.
According to the present invention, there is provided an impact detecting circuit which includes: a first integrating circuit and a second integrating circuit connected to both terminals of an impact detecting sensor for integrating outputs of both the terminals; a differential circuit for obtaining a difference between integrated outputs of the integrating circuits; and a comparator for outputting a detection signal when a differential output level of the differential circuit is at a threshold level and higher. The impact detecting circuit, together with the impact sensor, is used in a state of being included within an enclosure of a recording and reproducing apparatus, such as an HDD apparatus or the like.
In the thus formed impact detecting circuit or the recording and reproducing apparatus including the impact detecting circuit together with the impact sensor, when the input offset voltage occurs in the first and second integrating circuits, a large voltage waveform is generated at the output terminal of each of the integrating circuits. The voltage waveform is cancelled out by obtaining the difference by the differential circuit in the next stage. Thus, a signal resulting from the input offset voltage of the integrating circuits does not appear in the output terminal of the differential circuit.
In essential impact detection, on the other hand, when first-order differential currents in proportion to the strength of an impact are outputted from both the terminals of the impact sensor in opposite polarity, the currents are integrated by the first and second integrating circuits and converted into voltages with a flat frequency characteristic, and then a difference between the voltages is obtained by the differential circuit. In this case, since both the signals are of opposite polarity, the difference obtained between the signals appears in the output terminal of the differential circuit as a double-level signal. Then, the comparator compares the signal with the threshold level, whereby impact detection is performed.